1. Field of the Invention
The present invention relates to an abrasion detecting apparatus configured to detect abrasion of a component, such as a roller cutter, of a cutter head and a tunnel boring machine including the abrasion detecting apparatus.
2. Description of the Related Art
Conventionally, a cutter head of a tunnel boring machine configured to excavate hard ground, such as rock, is provided with roller cutters (also referred to as roller bits or disc cutters) configured to crush and excavate the ground. By pressing the roller cutters against the ground and rotating the cutter head, the rotating roller cutters crush a cutting face to excavate the hard ground.
In accordance with such tunnel boring machine, a cutting edge of each roller cutter abrades away as tunnel excavation proceeds. Therefore, an abrasion loss of the roller cutter is measured every time the tunnel boring machine excavates for a predetermined distance, and the roller cutter needs to be replaced with a new one if its abrasion loss exceeds an acceptable value.
Here, inventions have already been filed, in each of which the abrasion loss of the roller cutter is mechanically detected, and whether or not the roller cutter needs to be replaced with a new one is monitored by a tunnel boring machine main body. For example, the present applicant has already filed an application in which a detecting element is pressed against an outer periphery of the roller cutter by an oil-pressure jack, and the abrasion loss of the roller cutter is detected based on a change in a stroke of the oil-pressure jack (see Japanese Laid-Open Patent Application Publication No. 2003-74295, for example).
Moreover, there is another prior art in which a small jack is provided to be able to project and contact the cutting edge of the roller cutter, and the abrasion of the roller cutter is detected by observing the amount of projection of the small jack using an endoscope (see Japanese Laid-Open Patent Application Publication No. 6-117188, for example).
Further, there is yet another prior art in which the abrasion loss of the roller cutter is obtained such that: a magnetic scale is provided inside a hub which holds the roller cutter; a rotation detector is provided at a shaft; the rotation detector detects the number of rotations of the roller cutter; and the diameter of the cutter is calculated from the number of rotations (see Japanese Laid-Open Utility Model Application Publication No. 5-14299, for example).
Although this is not a technology which mechanically detects the abrasion loss of the roller cutter, there is still another prior art in which in order to prevent the cutter bit of a shield machine or an aboveground structure from being damaged such that the cutter bit hits an obstacle, such as a pile, an obstacle detecting bit is provided to project forward of the cutter bit, a fluid pressure supply system configured such that fluid pressure is released if the obstacle detecting bit drops off is adjacently provided, and a pressure detecting means detects the fluid pressure of the fluid pressure supply system to detect drop-off of the obstacle detecting bit (see Japanese Examined Patent Application Publication No. 6-63423).